All-cause mortality in New York, Maine, and Arizona dropped by nearly 6% over a 10-year period when Medicaid coverage was expanded, according to a study published in the New England Journal of Medicine.

Medicaid also improved access to care, and increased rates of self-reported health status of "excellent" or "very good" by more than 2%. "Policymakers should be aware that major changes in Medicaid – either expansions or reductions in coverage – may have significant effects on the health of vulnerable populations," the researchers said.

“Our study documents that large expansions of Medicaid eligibility in three states were associated with a significant decrease in mortality during a 5-year follow-up period, as compared with neighboring states without Medicaid expansions. Mortality reductions were greatest among adults between the ages of 35 and 64 years, minorities, and residents of poor counties. These findings may influence states' decisions with respect to Medicaid expansion under the ACA,” they reported.

Researchers looked at mortality rates in New York, Maine, and Arizona five years before and after the Medicaid expansions, and compared them with those in four neighboring states – Pennsylvania, Nevada, New Mexico, and New Hampshire – that did not put such expansions in place. But not everyone is convinced the researchers found something meaningful.

“They are trying really hard with the data that they have available, but at the end of the day it doesn’t really compensate for the fact that you don’t have the data you want, which is individual mortality rates and what happens to people with change in coverage over time,” Gail Wilensky, a health economist and former head of Medicare and Medicaid, commented to the New York Times.

In addition, when the researchers looked individually at each of the three states, the only state with a statistically significant decline was in the largest state, New York, and Wilensky questioned whether every state would have the same experience, the newspaper added.